Intermediate in sugar metabolism and in enzymatic carbohydrate degradation (alcoholic fermentation) where it is converted to acetaldehyde and CO2 by carboxylase. In muscle, Pyruvic acid (derived from glycogen) is reduced to lactic acid during exertion, which is reoxidized and partially retransformed to glycogen during rest. The liver can convert Pyruvic acid to alanine by amination. A diagnostic agent for Parkinson disease .